1. Field of the Invention
The present invention relates to a microfluidic chip for measuring the magnetic susceptibility of a superparamagnetic nanoparticle bead and droplet and a method for measuring magnetic susceptibility using the same.
2. Description of the Related Art
Superparamagnetic nanoparticle beads have been used in magnetic biosensors to detect the biomaterials to be analyzed. The superparamagnetic nanoparticle beads are materials which show magnetic properties upon the application of an external magnetic field, but lose the magnetic properties when the magnetic field is removed. Using the properties of such superparamagnetic nanoparticle beads, magnetic biosensors can detect biomaterials in liquid media, classify the type of biomaterial, and provide information on the position of the biomaterials. Thus, the magnetic properties of the superparamagnetic nanoparticle beads play an important role in determining the abilities of the biosensors, such as the ability to diagnose and resolve the biomaterial to be analyzed, and the ability to transport biomaterials.
The superparamagnetic nanoparticle beads are characterized in that they are magnetized by an externally applied magnetic field to produce a stray magnetic field (Hstray). For this reason, when the superparamagnetic nanoparticle beads are present around a sensor, the total effective magnetic field (Heff) in the sensor can be determined by the sum of vectors of an externally applied magnetic field (Happ) and an induced magnetic field generated from the superparamagnetic nanoparticle beads magnetized by the externally applied magnetic field (Happ).
Thus, using the characteristic in that a magnetic field in a magnetic biosensor changes depending on the presence or absence of superparamagnetic nanoparticle beads, the magnetic biosensor can sense magnetic resistance caused by the change of the magnetic field to detect the biomaterial to be analyzed.
The superparamagnetic nanoparticle beads are generally in a form in which superparamagnetic nanoparticles such as iron oxide (Fe3O4) or γ-iron oxide (γ-Fe2O3) nanoparticles are dispersed on spherical polymer matrices, and have a very small volume, and thus magnetic signals generated therefrom are also very fine. Accordingly, studies on the effective detection of magnetic signals from the superparamagnetic nanoparticle beads have been conducted.
Conventional methods for measuring the magnetic properties of superparamagnetic nanoparticle beads, such as their magnetic susceptibility, magnetic field dependence and saturation magnetization, include a method employing a superconducting quantum interference device (SQUID), a method employing a vibrating sample magnetometer, and the like.
PCT Patent Application No. PCT/US00/007829 discloses a method for measuring the magnetic susceptibility of a magnetic material using a superconducting quantum interference device. Specifically, PCT Patent Application No. PCT/US00/007829 discloses a method for measuring the magnetic susceptibility of a magnetic material using an apparatus comprising a superconducting material disposed on a flexible metallic substrate, a permanent magnet for applying a magnetic field, a superconducting quantum interference device, and a magnetic flux transformer. The above method has disadvantages in that, because the superconducting quantum interference device is used, a large number of control elements for performing the process are used, the method is not suitable for use for point-of-care testing due to elements that are used at very low temperatures, and high costs are incurred.
In addition, the method for measuring the magnetic susceptibility of superparamagnetic nanoparticle beads using a vibrating sample magnetometer comprises forming a strong magnetic field in a system to magnetize a sample, and measuring the susceptibility of the sample while vibrating the sample upward and downward. This method is not suitable for use for point-of-care testing, because it consumes a large amount of power.
In the above measurement methods, the magnetic susceptibility of a sample is measured using a nanoparticle bead cluster, which has a volume of about 100 μg and comprises 10,000 or more nanoparticles. Thus, in the above methods, the magnetic susceptibility of the nanoparticle bead cluster is measured, and the magnetic susceptibility of the nanoparticles is deduced from the results of the measurement. For this reason, there are limitations in the quantitative measurement or high-sensitivity measurement of each nanoparticle bead.
Meanwhile, with respect to methods for measuring the magnetic properties of a sample using superparamagnetic nanoparticle beads, studies as described below have been reported. For example, the literature [G. Mihajlovic, K. Aledealat, P. Xiong, S. v. Molnar, M. Field, G. J. Sullivan, “Magnetic characterization of a single superparamagnetic bead by phase-sensitive micro-Hall magnetometry”, Appl. Phys. Lett. 91 (2007) 172518] discloses a method of measuring the magnetic susceptibility of a superparamagnetic nanoparticle bead having a diameter of 1.2 μm, in which the magnetic susceptibility of the superparamagnetic nanoparticle bead is measured using a micro-sized semiconductor Hall sensor, in which the sensor element does not produce an induced magnetic field. Specifically, in this method, the magnetic susceptibility of the nanoparticle bead in a region to which a low magnetic field is applied is formulated by the Langevin function, and its value is obtained by fitting a curve to the Hall sensor output voltage versus an externally applied magnetic field, with the fitting parameters being the distribution median and the constituent magnetic nanoparticles. This method is characterized in that the curve of the Hall sensor output voltage versus the externally applied magnetic field is well fitted, because a single bead sample is used, unlike the method that uses the nanoparticle bead cluster as a sample.
In addition, magnetic sensors are used in various fields to sense magnetic fields, store data, sense the position of proximity switches, sense speed, and sense electric currents.
Magnetoresistive sensors have high sensitivity even in a very low magnetic field at room temperature and can be used to sense biomolecules (P. P. Freitas, R. Ferreria, S. Cardoso and F. Cardoso, “Magnetoresistive sensors”, J. Phys.: Condens. Matter 19, 165221 (2007), D. L. Graham, H. A. Ferreira and P. P. Freitas, “Magnetoresistive-based biosensors and biochips”, Trends Biotechnol. 22, 455 (2004), B. Srinivasan, Y. Li, Y. Jing, Y. Xu, X. Yao, C. Xing and J. Wang, “A detection system based on giant magnetoresistive sensors and high-moment magnetic nanoparticles demonstrates zeptomole sensitivity: potential for personalized medicine” Angew. Chem. Int. Ed. 48, 2764 (2009), R. S. Gaster, L. Xu, S. Han, R. J. Wilson, D. A. Hall, S. J. Osterfeld, H. Yu and S. X. Wang, “Quantification of Protein Interactions and Solution Transport Using High-Density GMR Sensor Arrays” Nature Nanotech. 6, 314 (2011), R. S. Gaster, D. A. Hall, C. H. Nielsen, S. J. Osterfeld, H. Yu, K. E. Mach, R. J. Wilson, B. Murmann, J. C. Liao, S. S. Gambhir and S. X. Wang, “Matrix-insensitive protein assays push the limits of biosensors in medicine”, Nature Med. 15, 1327 (2009), Y. Li, B. Srinviasan, Y. Jing, X. Yao, M. A. Hugger, J. Wang and C. Xing, “Nanomagnetic competition assay for low-abundance protein biomarker quantification in unprocessed human sera”, J. Am. Chem. Soc. 132, 4388 (2010)). When a protein, an antibody or a nucleic acid is attached to nanoparticles or nanoparticle beads which are immobilized onto the surface of magnetic sensors, it can assist in finding molecules. Many types of magnetic nanoparticles perform roles such as biological labels in colloidal suspensions and can be integrated according to functions and application fields (D. L. Graham, H. A. Ferreira and P. P. Freitas, “Magnetoresistive-based biosensors and biochips”, Trends Biotechnol. 22, 455 (2004)). Superparamagnetic nanoparticles having a size of 10 nm have no remnant magnetism and show good dispersibility. Magnetic fluids are stable colloidal suspensions of magnetic nanoparticles.
Most initial studies were focused on improving the detection limit of magnetic sensors in magnetic fields. Many kinds of sensors have been developed, including giant magnetoresistive (GMR) sensors, anisotropic magnetoresistive (AMR) sensors, semiconductor Hall sensors, planar Hall resistive (PHR) sensors, and magnetic tunnel junctions (MTJs) (D. L. Graham, H. A. Ferreira and P. P. Freitas, “Magnetoresistive-based biosensors and biochips”, Trends Biotechnol. 22, 455 (2004)). These sensors can sense even single magnetic nanoparticle beads and include semiconductor Hall sensors (P. Besse, G. Boero, M. Demierre, V. Pott and R. Popovic, “Detection of a single magnetic microbead using a miniaturized silicon Hall sensor”, Appl. Phys. Lett. 80, 4199 (2002)), magnetic tunnel junctions (MTJs) (W. Shen, X. Liu, D. Mazumdar and G. Xiao, “In situ detection of single micron-sized magnetic beads using magnetic tunnel junction sensors”, Appl. Phys. Lett. 86, 253901 (2005)), and planar Hall effect sensors (L. Ejsing, M. F. Hansen, A. K. Menon, H. A. Ferreira, D. L. Graham and P. P. Freitas, “Planar Hall effect sensor for magnetic micro- and nanobead detection”, Appl. Phys. Lett. 84, 4729 (2004)). Measurement systems have developed toward the use of a lock-in amplifier to increase signal-to-noise ratio.
For application to biosensors, systems comprising a magnetic sensor integrated with a microfluidic system (P. Besse, G. Boero, M. Demierre, V. Pott and R. Popovic, “Detection of a single magnetic microbead using a miniaturized silicon Hall sensor”, Appl. Phys. Lett. 80, 4199 (2002)) have been developed. When magnetic nanoparticle beads and nanoparticles are exposed on the sensor, a magnetic signal is measured as an electrical signal. The sensor integrated with the microfluidic system can sense the nanoparticles and nanobeads that flow.
When a valve, a pump and a mixer together with a magnetic sensor are added to a microfluidic system, an automated and complex analysis system can be developed.
Magnetic fluids have been widely used in experiments on the performance of magnetic materials (L. Ejsing, M. F. Hansen, A. K. Menon, H. A. Ferreira, D. L. Graham and P. P. Freitas, “Planar Hall effect sensor for magnetic micro- and nanobead detection”, Appl. Phys. Lett. 84, 4729 (2004)). Most reported magnetic fluid signals had problems in that slowly flowing signals were sensed, the sensed signals were weak, and the time resolution of the signals was also poor.
Accordingly, the present inventor has developed a microfluidic chip including a planar Hall resistive sensor and has found a method for measuring the magnetic susceptibility of a superparamagnetic nanoparticle bead and droplet in a flowing magnetic fluid using the microfluidic chip, thereby completing the present invention.